1. Field of the Invention
The present invention relates to a solid electrolytic capacitor element, a manufacturing method of the solid electrolytic capacitor element, and a solid electrolytic capacitor. In particular, the present invention relates to an element using niobium oxide as a dielectric, manufacturing method of the element, and the solid electrolytic capacitor.
2. Description of the Related Art
Conventionally, it has been known as a solid electrolytic capacitor using niobium oxide (Nb2O5, or niobium pentoxide) formed by anodizing metal niobium, as a dielectric layer (for example, refer to Japanese Unexamined Application No. 52-39164).
FIG. 1 is a cross-sectional view for explaining a structure of a conventional solid electrolytic capacitor. With reference to FIG. 1, the structure of the conventional solid electrolytic capacitor will be explained.
In the conventional solid electrolytic capacitor, as shown in FIG. 1, an anode 101 is provided with an anode lead 101a, and a cuboid base substance 101b formed of a porous sintered body of niobium particles. The anode lead 101a has a part buried in the base substance 101b. 
On the anode 101, an oxide layer 102 formed of Nb2O5 is formed so as to cover the base substance 101b. Here, the oxide layer 102 functions as what is called a dielectric layer.
On the oxide layer 102, a conductive polymer layer 103 formed of polypyrrole and the like is formed so as to cover the oxide layer 102. Here, the conductive polymer layer 103 functions as what is called an electrolyte layer.
On the conductive polymer layer 103, a cathode 104 having a laminated structure is formed. The laminated structure includes a first conductive layer 104a including carbon particles and formed so as to cover the conductive polymer layer 103; and a second conductive layer 104 including silver particles and formed so as to cover the first conductive layer 104a. 
A conductive adhesive layer 105 is formed on the cathode 104. Moreover, a cathode terminal 106 is formed on the conductive adhesive layer 105. Additionally, an anode terminal 107 is connected onto the anode lead 101a exposed through the base substance 101b and the oxide layer 102.
Furthermore, a mold external packaging resin 108 is formed on the cathode 104, the cathode terminal 106 and the anode terminal 107. End portions of the cathode terminal 106 and the anode terminal 107 are pulled out to the outside. Thereby, the conventional solid electrolytic capacitor is configured.
FIGS. 2 to 6 are cross-sectional views for explaining processes for forming the conventional solid electrolytic capacitor. Next, with reference to FIGS. 2 to 6, descriptions will be provided for processes for forming the conventional solid electrolytic capacitor having a structure as mentioned above.
First, as shown in FIG. 2, the anode 101 provided with the anode lead 101a and the cuboid base substance 101b is formed. The base substance 101b is formed of a porous sintered body of niobium particles and is formed by sintering a compact in a vacuum. The compact is formed of niobium particles, and a part of the anode lead 101a is buried in the compact.
Next, as shown in FIG. 3, by anodizing the anode 101 in a solution of phosphoric acid and the like, the oxide layer 102 of Nb2O5 is formed on the base substance 101b so as to cover the basic substance 101b. 
Subsequently, as shown in FIG. 4, the conductive polymer layer 103 of polypyrrole and the like is formed, for example, by polymerizing pyrrole so as to cover the oxide layer 102.
Next, as shown in FIG. 5, the first conductive layer 104a including carbon particles is formed by applying and drying carbon paste on the conductive polymer layer 103 so as to cover the conductive polymer layer 103. Thereafter, the second conductive layer 104b including silver particles is formed by applying and drying silver paste on the first conductive layer 104a so as to cover the first conductive layer 104a. Thereby, the cathode 104, which has a laminated structure, is formed. The laminated structure includes the first conductive layer 104a and the second conductive layer 104b in a manner covering the conductive polymer layer 103.
Thereafter, as shown in FIG. 6, a conductive adhesive layer 105, which connects the cathode 104 and the cathode terminal 106 with each other, is formed. The conductive adhesive layer 105 is formed by adhering the cathode terminal 106 onto the cathode 104 with a conductive adhesive applied on the cathode terminal 106, and by drying this conductive adhesive. Additionally, the anode terminal 107 is welded onto the anode lead 101a exposed through the base substance 101b and the oxide layer 102.
Finally, as shown in FIG. 1, the mold external packaging resin 108 is formed on the cathode 104, the cathode terminal 106 and the anode terminal 107. The end portions of the cathode terminal 106 and the anode terminal 107 are pulled out to the outside. Thus, the conventional solid electrolytic capacitor is formed.